| Persistent winter-time heavy haze episodes caused by anthropogenic aerosols have repeatedly shrouded North China in recent years,while natural dust from west and northwest of China also frequently affects air quality in this region.The traditional air pollution observing technology mainly relies on surface sampling,which makes it difficult to realize the vertical evolutionary research of compound air pollutants.In order to timely grasp the transmission,accumulation and dissipation of various air pollutants in the Beijing-Tianjin-Hebei region(BTH),and to quantify the contribution of natural and anthropogenic sources to air pollution,precise observation of aerosol types,aerosol vertical structure and optical properties is needed.LIDAR,as a paradigm of atmospheric optical remote sensing technology,can not only obtain the spatial and temporal distribution of air pollutants in a timely and rapid manner,but also combine polarization channels and Raman channels to obtain a variety of aerosol optical parameters to investigate the vertical structure evolution,and regional transport characteristics of air pollutants.This dissertation carried out a study of aerosol optical parameter profile inversion algorithm based on dual-wavelength polarization Raman lidar,and also classified aerosols in the BTH region based on aerosol optical parameters,quantified the contribution of regionally transmitted natural dust and anthropogenic pollutants to air pollution,revealed the role of dust aerosols in heavy winter air pollution in the BTH region,and gained insight into the sources,accumulation and dissipation process of heavy air pollution.The main findings are as follows.1.Inversion of atmospheric extinction coefficient,backscattering coefficient,lidar ratio,particle depolarization ratio,extinction color ratio,and water vapor mixing ratio based on elastic and inelastic backscattering signals from atmospheric aerosols and molecules.Subsequently,the uncertainty of the optical parameter inversion is evaluated directly from the most primitive solution of the error,based on the signal-to-noise ratio of the backscatter signal and the model or empirical parameters entered in the inversion.It is also compared with the sounding balloon,sun photometer,MAX-DOAS,and CALIPSO data to verify the accuracy of the aerosol optical parameters inversion algorithm.2.The primary aerosol types and their contributions to air pollution in the BTH region were determined based on aerosol optical parameters.Three aerosol types can be classified,natural dust,anthropogenic aerosols,and the mixture of anthropogenic aerosols and dust(polluted dust).The classification results are basically consistent with the classification results from CALIPSO satellite measurements.The classification results show that approximately 45%of aerosols below 1.8 km are contributed by polluted dust during our one year observations.The contribution of dust increased with height,from 6%to 28%,while the contribution of anthropogenic aerosols decreased from 49%to 25%.In addition,polluted dust is the major aerosol subtype below 1.0 km in spring(over 60%)and autumn(over 70%).Anthropogenic aerosols contribute more than 75%of air pollution in summer.In winter,anthropogenic aerosols prevailed(over 80%)in the planetary boundary layer(PBL),while polluted dust(around 60%)dominated the upper PBL.3.We found that wintertime aerosols in BTH region are typically characterized by a pronounced vertical stratification,where scattering non-spherical particles(dust or mixtures of dust and anthropogenic aerosols)dominated above the PBL,and absorbing spherical particles(anthropogenic aerosols)prevailed within the PBL.This stratification is governed by meteorological conditions that strong northwesterly winds usually prevailed in the upper PBL,and southerly winds are dominated in the PBL.Model results show that,besides directly deteriorating air quality,the key role of the elevated dust is to depress the development of PBL and weaken the turbulence exchange,and it is more obvious during dissipation stage,thus inhibiting the dissipation of heavy surface anthropogenic aerosols.The dust-meteorology interactions provide very important information toward a complete understanding of the formation mechanism of winter haze in BTH region,and may also explain the special multiphase chemistry in this region,thus providing a scientific basis for the formulation of air pollution prevention and control policies in the BTH region.4.The contributions of dust and anthropogenic aerosols to the backscattering coefficient in polluted dust were separated based on aerosol optical parameters.The contribution of natural dust and anthropogenic aerosol to air quality in Beijing from cross-regional transmission was quantified by taking the air pollution during the 2019 National Day parade as an example.The contributions of local emissions to air pollution during the 2019 National Day parade were insignificant,mainly affected by regional transport,including anthropogenic aerosol in North China plain and Guanzhong Plain(Hebei,Tianjin,Shandong,and Shanxi),and dust aerosol in Mongolia regions and Xinjiang.Moreover,the cross-regional transmission of natural dust dominated the air pollution during the 2019 National Day parade,with a relative contribution to particulate matter mass concentrations exceeding 74%below 4 km.Our results highlight that controlling anthropogenic emissions over regional scales and focusing on the effects of natural dust is crucial and effective to improve Beijing’s air quality. |
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